A set screw has been widely used as a fastener for fixing or fastening two members to each other. When the two members are fixed to each other with the set screw, in general, a positioning hole is formed in one member and a female thread is formed in the other member. In a state in which center axes of the female thread and the positioning hole coincide with each other, the two members are positioned and the set screw is screwed into the female thread from a female thread side to a position where a distal end of the set screw enters the positioning hole, thereby the two members are fixed to each other. Commonly, a female thread is formed on a member having a wider space so as not to hinder fastening work by a fastening tool. For example, when two cylindrical members are fixed, a female thread is formed in a member on a radially outer side. A general fixing method in fixing the two cylindrical members in this way is described with reference to FIG. 11.
FIG. 11 is a schematic sectional view showing a fixing structure with a set screw according to a conventional example. In the example shown in the figure, a cylindrical first member 610 and a cylindrical second member 620 are fixed to each other with a set screw 700. A positioning hole 611 is formed in an outer circumferential surface side of the first member 610. A female thread 621 is formed in the second member 620. When the first member 610 and the second member 620 configured as described above are fixed, first, the second member 620 is made to slide with respect to the first member 610 to match the center axes of the female thread 621 and the positioning hole 611. In this state, the set screw 700 is screwed into the female thread 621 to a position where a distal end of the set screw 700 enters the positioning hole 611. Consequently, the second member 620 becomes unable to move in both an axial direction (a direction of the center axis of the first member 610 and the second member 620) and a rotating direction with respect to the first member 610. Therefore, the first member 610 and the second member 620 are fixed to each other.
However, in the case of such a fixing structure, the female thread 621 has to be formed in the second member 620 provided on the radially outer side. The inner diameter of the female thread 621 has to be set according to the dimension of the set screw 700; hence, commonly, a shaft portion side of the set screw 700 is in an exposed state. Consequently, in some cases, not only its appearance but also its function may be adversely affected.
For example, in a sealing structure including a mechanical seal, there is known a technique for, in order to cause a fluid to flow, fixing an annular partial impeller on the outer circumference of a sleeve attached to a rotating shaft (see Patent Literature 1). In this technique, the partial impeller is fixed to the sleeve with a set screw. A plurality of grooves are formed on the outer circumferential surface of the partial impeller in order to cause fluid to flow according to the rotation of the partial impeller. Therefore, in order to fix the set screw from the outer circumference surface side of the partial impeller, a female thread has to be formed in a position between the grooves, or in the groove. Therefore, in some cases, the grooves may be joined by the female thread depending on the dimension of the inner diameter of the female thread. In some cases, a part of a shaft portion of the set screw projects into the grooves and a part of the grooves is closed by the shaft portion. In these cases, the ability of the partial impeller to cause the fluid to flow is deteriorated.
In the structure shown in FIG. 11, in a case when the first member 610 and the second member 620 rotate, there is also a problem in that, if the set screw 700 loosens, the set screw 700 gradually comes off the female thread 621 due to a centrifugal force. The sealing structure described above also has this problem.